In manufacturing processes which use a vapor deposition technique, a vapor of a metal such as gold is created within a vacuum chamber which contains the workpiece. The workpiece is held on a movable stage such that it may be moved relative to a window which is typically a quartz plate in the wall of the vacuum chamber. In order to deposit the gold onto the substrate, a laser beam is used to locally heat a very, very small region of the silicon substrate. The heating of the substrate creates a condition and environment which permits the gold molecules to deposit out of the vapor form onto the surface of the silicon substrate.
The gold molecules, when deposited on the silicon substrate, may create electrical conductors on the insulations. In order to create extremely fine electrically conductive paths on the insulation surface of the silicon, it is necessary to very, very finely focus the laser beam while at the same time passing the focused laser beam through the quartz plate which serves as the window into the working vacuum chamber.
Since the lens elements must all remain outside the vacuum chamber, it is necessary for the lens assembly to have a sufficiently long back working distance between the exit or last element and the focal point such that the focused beam may be passed through the quartz plat and sufficiently inside the vacuum chamber to focus on the surface of the silicon slab where the gold molecules of the gold vapor are to be deposited. The reverse telephoto nature of a lens displaces the principle point outside the lens assembly providing a longer back working distance between the lens assembly and the focal point, while maintaining a relatively short focal length.
In order to project the maximum amount of illumination from the laser and the laser beam onto the focus point within the vacuum chamber of the vapor deposition device, it is necessary to expand the laser beam as received from the laser from a 1.6 millimeter diameter to approximately a 10.8 millimeter diameter where the beam enters the reverse telephoto objective lens of this invention. By expanding the beam to that diameter, the maximum beam diameter may be then introduced into the reverse telephoto lens thus causing the maximum controllable focus into an extremely fine point of approximately 3.14 microns airy disk diameter. Lenses for such expansion are known in the art.